In a mobile communication system defined in the 3GPP, when a mobile station UE performs an Inter-RAT (Radio Access Technology) handover between a cell of the E-UTRAN (Evolved Terrestrial Radio Access Network) scheme and a cell of the UTRAN scheme, a radio access apparatus of a handover source (for example, a radio network controller RNC and a radio base station eNB) can transfer downlink data destined for the mobile station UE which is transmitted from a serving gateway apparatus S-GW to a radio access apparatus of a handover target, as illustrated in FIG. 15.
However, in a conventional mobile communication system, a radio access apparatus of a handover target is configured to receive not only the downlink data transferred from the radio access apparatus of a handover source as described above but also receive downlink data transmitted from the serving gateway apparatus S-GW.
In such a case, however, the radio access apparatus of a handover target cannot easily distinguish between the downlink data transferred from the radio access apparatus of a handover source and the downlink data transmitted from the serving gateway apparatus S-GW, resulting in a problem that it is difficult to perform a reordering control of the both data.
Therefore, the present invention is intended to overcome the above-described problem. An object of the present invention is to provide a mobile communication method, a radio access apparatus, and a gateway apparatus, capable of performing a reordering control of downlink data in a radio access apparatus of a handover target when performing an Inter-RAT handover.